Various photosensitive resin-compositions are known, and are widely used in various applications, e.g., as printing plates, color proofs, resists for producing printed circuit frames, color filters and the like. Those compositions form images by undergoing processing operations depending on their intended use. In many cases, the processing operations basically comprise imagewise pattern exposure and development-processing. Methods for the development-processing are classified roughly into those using organic solvents as a developer and those using alkaline aqueous solutions as a developer. In recent years, however, methods of using alkaline aqueous solutions have prevailed over those using organic solvents from the viewpoint of environmental conservation safety in the working environment, and the like.
Therefore, a large number of binder resins soluble in an alkaline aqueous solution have been developed and used for photosensitive resin compositions. Examples of such binder resins include poly(meth)acrylic acid, polycinnamic acid, polymaleic acid, polymaleic anhydride, polyitaconic acid and like homopolymers, and copolymers prepared from the above-noted monomers and various other monomers.
Specific examples of such resins include methacrylic acid copolymers, acrylic acid copolymers, itaconic acid copolymers, crotonic acid copolymers, maleic acid copolymers and partially esterified maleic acid copolymers as described in JP-B-59-44615 (the term "JP-B" as used herein means an "examined Japanese patent publication), JP-B-54-34327, JP-B-58-12577, JP-B-54-25957, JP-A-59-53836 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-A-59-71048, JP-A-60-159743, JP-A-60-258539, JP-A-01-152449, JP-A-02-199403 and JP-A-02-199404, and cellulose derivatives containing carboxyl groups in their side chains.
When the above described polymers are used as binder resins, alkali-soluble groups, such as carboxyl groups, are still present in the areas remaining after development (i.e., the areas insoluble in an aqueous alkaline solution, e.g., the areas which have become resistant to an alkaline developer by reaction with a polyfunctional monomer, a cross-linking agent, a binder containing cross-linking groups or the like). Accordingly, the resistance of the remaining areas to an aqueous alkaline solution is insufficient when alkali treatment is carried out for a longer time or when the aqueous alkaline solution has a pH that is higher than that of the developer. However, if the content of alkali-soluble groups in a binder resin is reduced in order to enhance the alkali resistance of the remaining areas, the developability of the resulting binder resin in an aqueous alkaline solution is reduced. Therefore, it is difficult for conventional alkali-soluble resins to provide both good developability in an aqueous alkaline solution and a high level of alkali resistance in the remaining areas after development.
A photosensitive resin composition capable of providing both alkali developability as described above and a high level of alkali resistance in the areas remaining after development is well adapted for use as a protective layer of a color filter.
A color filter is one of the important parts of a liquid crystal display panel, and various performance items are required thereof. In particular, heat resistance and chemical resistance are very important when a color filter is used in an STN (Super Twisted Nematic) liquid crystal display panel or a FLC (Ferroelectric Liquid Crystal) display panel. This is because a transparent conductive layer is formed on the color filter and subsequently shaped into a transparent electrode pattern.
More specifically, the liquid crystal display panel described above has a multicolor picture-element layer on a transparent substrate which is generally made of glass. The multicolor picture-element layer is generally composed of red, green and blue picture elements which are alternately arranged in matrix form. The dimensions of each picture element, though they depend on the intended use, is on the order of 10-100 .mu.m by 50-400 .mu.m. The shape thereof is not necessarily a rectangle of the foregoing dimensions, but may be modified into the desired shape depending on the intended use. Furthermore, a black-colored or light-shielding black matrix may be formed so as to border each picture element and the peripheral part, if desired. Moreover, a protective layer is formed on the multicolor picture-element layer, to thereby obtain a color filter.
A transparent conductive layer is generally formed by sputtering ITO (indium tin oxide) on the protective layer. In the case of STN and ferroelectric liquid crystal display panels, the transparent conductive layer is further shaped into a transparent electrode pattern by photolithography, to thereby attach electrodes to the color filter. In addition, an oriented film is formed on the electrode-attached color filter. The thus prepared color filter and a separate transparent substrate which is provided with transparent electrodes and an oriented film are sealed, and a prescribed gap is kept therebetween by use of a spacer. Then, a liquid crystal is injected into the gap formed between the two substrates, to thereby produce a panel.
In a series of processes for forming the color filter of a liquid crystal display panel, it is necessary for the protective layer formed on the multicolor picture-element layer to have the following properties: (1) evenness, (2) sufficient hardness to prevent the spacer, which is used for securing the gap of a liquid crystal cell, from sinking therein, (3) resistance to various chemicals (including solvents for photoresist, acidic etching solutions, strongly alkaline resist stripping solutions, solvents for the coating solution of an oriented film, and the like) used in photolithographic operations performed on a transparent conductive layer, (4) transparency in the visible region as well as no fog and no turbidity, (5) excellent adhesion not only to a multicolor picture-element layer but also to a substrate, because in some cases the protective layer is provided directly on a substrate having no multicolor picture elements thereon, and (6) photosensitivity to enable the protective layer to be patterned by development (that is, the properties of a photosensitive resin) for the reason that only unnecessary areas (e.g., the areas on the scribe line) of the protective layer can be removed from the transparent substrate in high accuracy.
Examples of known light-sensitive materials which can serve as a protective layer when provided on a multicolor layer by a coating method or the like, exposed to light and then developed, include the UV curable resins described in JP-A-57-42009 and JP-A-60-244932, the vinylcarbonyl group containing polymers described in JP-A-59-7317, the photosensitive resins composed of PVA and sensitizers described in JP-A-59-184325, the gum-resin described in JP-A-60-42704, and the photosensitive resin composition obtained by removing the pigment from the pigment-dispersed photosensitive resin composition applied to the colored layer in JP-A-02-191901.
The protective layer is most desirably developable with an alkaline aqueous solution. This is advantageous in health and public hazard counter-measures. Furthermore, the protective layer desirably provides still greater alkali resistance when cured through the processes of exposure, development and heat treatment. This type of desirable protective layer can be obtained by using the compositions described, e.g., in JP-A-03-126950, JP-A-52-132091, JP-B-04-20923, JP-A-05-265208, Japanese Patent Application Nos. 5-152278, 5-202272, 6-1769 and 6-1766, etc.
In addition, light-sensitive materials comprising the combination of the resins used in the above-cited compositions with naphthoquinonediazide compounds as a sensitizer are disclosed, e.g., in JP-A-06-14888 and JP-A-04-347858.
All the resins used in the above-cited compositions are resins containing half-amide group obtained by reacting a maleic or itaconic anhydride copolymer with amines. However, it is hard to polymerize maleic or itaconic anhydride alone, as shown by the copolymerization reactivity ratios and other factors in Polymer Handbook II, 3rd Edition, page 153, compiled by J. Brandrup and H. Immergut, published by John Wiley & Sons. Inc. (1989). Also, maleic or itaconic anhydride and other monomers on the whole are not easily copolymerized, except that such monomers can readily copolymerize with a particular monomer such as styrene, vinyl acetate or the like to form an alternate copolymer. Therefore, it is difficult to easily produce a resin having the desired properties (including alkali developability, alkali resistance, and strong physical properties of the film before and after exposure) by controlling the compositional ratio between maleic or itaconic anhydride and other monomers.
Other resins having half-amido groups include known polyamic acid resins obtained by a polyaddition reaction between tetracarboxylic acid anhydrides and diamine compounds. However, the solubilities of these resins are difficult to control. The solubilities thereof are also very low, with the exception of special solvents having high polarity, such as NMP (N-methylpyrrolidone). Accordingly, these resins have a limited range of use.
Other resins having half-amido groups and which are resins comparable to the resins of the present invention are disclosed in JP-A-60-218662. However, these resins having half-amido groups are used as one component of a toner-dispersed liquid developer for electrostatic photography, and there is no description of their application to a photosensitive resin composition.
Furthermore, JP-A-01-197753, JP-A-62-279333, JP-A-62-136644, JP-A-62-5238, JP-A-61-252544, JP-A-61-57943, JP-A-61-177451 etc., describe resins containing half-amido groups. In any of these resins, however, the half-amido groups are contained as part of the skeleton of a dye precursor used for a silver halide photosensitive material. Therefore, the above-cited references are silent regarding alkali developability, the alkali resistance acquired after heating due to the presence of half-amido groups in these resins, and application of these resins to photosensitive resin compositions.
Such being the case, photosensitive resin compositions which are soluble in an aqueous alkaline solution, which can acquire sufficiently high alkali resistance after heating, and which possess excellent solubility, production suitability and chemical resistance have not hitherto been known.